CA1150816A - Method and apparatus for implanting a charge in an electret foil - Google Patents
Method and apparatus for implanting a charge in an electret foilInfo
- Publication number
- CA1150816A CA1150816A CA000354480A CA354480A CA1150816A CA 1150816 A CA1150816 A CA 1150816A CA 000354480 A CA000354480 A CA 000354480A CA 354480 A CA354480 A CA 354480A CA 1150816 A CA1150816 A CA 1150816A
- Authority
- CA
- Canada
- Prior art keywords
- foil
- electret
- electrodes
- electric field
- path
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000011888 foil Substances 0.000 title claims abstract description 98
- 238000000034 method Methods 0.000 title claims abstract description 34
- 230000005684 electric field Effects 0.000 claims abstract description 30
- 230000001965 increasing effect Effects 0.000 claims abstract description 7
- 238000010924 continuous production Methods 0.000 claims description 2
- -1 polytetrafluoroethylene Polymers 0.000 claims description 2
- 229920001343 polytetrafluoroethylene Polymers 0.000 claims description 2
- 239000004810 polytetrafluoroethylene Substances 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 4
- 238000009826 distribution Methods 0.000 description 3
- 239000000523 sample Substances 0.000 description 3
- 229920006362 Teflon® Polymers 0.000 description 2
- PBAYDYUZOSNJGU-UHFFFAOYSA-N chelidonic acid Natural products OC(=O)C1=CC(=O)C=C(C(O)=O)O1 PBAYDYUZOSNJGU-UHFFFAOYSA-N 0.000 description 2
- 230000000750 progressive effect Effects 0.000 description 2
- 229920002799 BoPET Polymers 0.000 description 1
- 239000005041 Mylar™ Substances 0.000 description 1
- 239000004809 Teflon Substances 0.000 description 1
- 238000002513 implantation Methods 0.000 description 1
- 229920000515 polycarbonate Polymers 0.000 description 1
- 239000004417 polycarbonate Substances 0.000 description 1
- 229920000136 polysorbate Polymers 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- HLCHESOMJVGDSJ-UHFFFAOYSA-N thiq Chemical compound C1=CC(Cl)=CC=C1CC(C(=O)N1CCC(CN2N=CN=C2)(CC1)C1CCCCC1)NC(=O)C1NCC2=CC=CC=C2C1 HLCHESOMJVGDSJ-UHFFFAOYSA-N 0.000 description 1
- 238000011144 upstream manufacturing Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G7/00—Capacitors in which the capacitance is varied by non-mechanical means; Processes of their manufacture
- H01G7/02—Electrets, i.e. having a permanently-polarised dielectric
- H01G7/021—Electrets, i.e. having a permanently-polarised dielectric having an organic dielectric
- H01G7/023—Electrets, i.e. having a permanently-polarised dielectric having an organic dielectric of macromolecular compounds
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Treatments Of Macromolecular Shaped Articles (AREA)
- Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
Abstract
ABSTRACT
In previously proposed arrangements for charging an electret foil the electret charge implanted varies over the area of the foil. In order to promote more even charging of the foil, the method of the invention subjects the foil to a progressively increasing electric field. One form of apparatus used to carry out the method has rollers at progressively higher potentials and electric fields are applied across the foil between these rollers and a metallized layer on the rear face of the foil which is earthed by a roller.
In previously proposed arrangements for charging an electret foil the electret charge implanted varies over the area of the foil. In order to promote more even charging of the foil, the method of the invention subjects the foil to a progressively increasing electric field. One form of apparatus used to carry out the method has rollers at progressively higher potentials and electric fields are applied across the foil between these rollers and a metallized layer on the rear face of the foil which is earthed by a roller.
Description
1150~16 ThiQ invention relate~ to a method and apparatu~
for implanting an electret charge into a foil capable of retaining an effective electret charge.
It has been proposed to charge a strip of electret foil by passing one face of the ~trip over an electrode connected to a source of high voltage while making electrical contact with the other face of the strip so that an electric field is applied acros~ the foil.
Normally the electric field is applied while the electret foil i8 at an elevated temperature but in our copending British patent application No. 34018/78 published on 28th February 1979 under No. 2002961, there i~ de~cribed a proposal for charging a st~ip of electret foil at room temperature in which the electrode over which the strip is passed i~ a knife edge.
We have found that there are some disadvantage~
with the~e proposed charging methods. Fir~t we have found that the magnitude of the electret charge implan-ted into the material will vary from one batch of material to another, even though the charging conditions are apparently identical. Secondly, we have found that within a single strip of film there is a variation over the width and length of the strip of the magnitude of implanted electret charge. When the electret foil i8 employed, for example in the production of microphone transd~cers, the variation in electret charge of the foil resultQ in variation in the sen itivity of the tranQducers and either this variation has to be ' 1150~16 tolerated or the transducers have to be individually te~ted adding significantly to their manufacturing co~t.
It i~ an object of the invention to provide an improved method and apparatus for implanting an electret charge into a foil capable of retaining an effective electret charge.
According to the invention there is provided a method of implanting an electret charge into a foil capable of retaining an effective electret charge, - the method including applying a fir~t electric field and thereafter a second electric field acro~s the foil, the Qecond electric field being of greater magnitude than the first, whereby an effective electret charge is implanted into the foil.
We have found that the uneven electret charging mentioned above arises because during the manufacturing process the foil has an adventitiou~ electret charge implanted into it due to the high electrostatic voltage~
produced during mechanical handling and rolling of the foil. Any area of the foil that has this adventitious elect~et charge in it before charging will in the fir~t charging proces~ accept a different amount of charge from the knife edge than a non-charged area of foil, ~ince the effective electric field applied to the adventitiously charged area differs from that applied to the non-charged area. By charging the foil progres-sivel~f all of the foil is first charged to not less than ., , about the highest electret charge implanted during manufacture and i~ then further charged to the required final level. Since for the further charging, the foil starts with a relatively even electret charge the final charge implanted into the foil is very much more even than if the foil i8 subjected to only one electric fie~d.
Preferably at lea~t three electric fields are applied successively across the foil, the magnitude of the electric field~ increasing progre~ively, In one 10 embodiment of the invention five electric fields are applied ~uccessively across the foil. With five electric fields the implantation of charge is-Qubstantially even over the whole width and length of the electret foil.
In~tead of applying a succession of discrete and progressively greater electric fields to the electret foil, the magnitude of the electric field may be increased continuously from a fir~t value up to the maximum electric field to be applied.
The method may ~e carried out as a continuous 20 process. In this ca~e the charging of the foil in a succes~ion of discrete stage~ may be achieved by passing the electret foil over a series of electrodes maintained at progreQsively higher positive or negative potentialQ.
The charging of the foil by a continuously increasing electric field may ~e achieved ~y passing the electret foil over the surface of a resistive element having one end maintained at a higher positive or negative potential than the other end, there being a contin~ou~
11508~6 change in potential along the element from one end to the other.
As an alternative, the method may be carried out by pas~ing the foil over an electrode at a fir~t po-~itive or negative potential and then passing the foil over the same electrode at a second positive or negative potential higher than the first potential.
The greatest electric field applied acro~s the electret foil may lie in the range of from about 30 to 1o about 100 MV/m. In the case of a foil of 12.5 mm thick-ness this field is achieved by applying from about 375 to about 1250 volt~ across the foil.
The electrodes by which the electric fields are applied may be electrically conducting rollers.
The foil may be provided with a metallised surface on one face and this face may be pas3ed over an electri-- cally conducting roller by which the electric field is applied. The electrically conducting roller may be at earth potential.
The electret foil may be polytetrafluoroethylene, for example that sold under the trademark FEP Teflon.
Alternative materials which may for example be u~ed are polycarbonates or Mylar (RTM).
According to another aspect of the invention there is provided an electroacoustic transducer including an elec-tret foil as defined a~ove. The transducer may be incorporated in a telephone.
According to another aQpect of the invention there is provided an apparatu~ for implanting an effective electret charge into a foil capRble of retaining an effective electret charge, the apparatu~ including:
mean~ defining a path for a Qtrip of foil, a plurality of electrode-~ disposed along one ~ide of the path of the foil for making electrical contact with one face of the ~trip of foil, electrical contact mean~ on the-other side of the path for making electrical contact with the other face of the strip of foil, and means for applying a voltage between the elec-trodes and the electrical contact mean~, the arrange-; ment being such that the voltage applied to the electrode-~ is of greater magnitude towards the down-stream end of the path.
The plurality of electrode~ preferably comprises at lea~t three electrodes, the voltage applied to the electrode~ increaQing progre~ively towards the downQtream end of the path. The electrode~ may each be connected to a reQpective point in a potential divider network.
'`~' ~150816 A ~irQt spool ma~ be provided at the beginning oi the path for storing a strip of foil to be treated. A
second spool may be provided at the end of the path ~or recei~ing the ætrip of foil after treatment. The second spool may be connected to drive means to draw foil along the path. The first spool may be provided with a brake for ten~ioning foil along the path.
An electro~tatic measuring probe ma~ be located adjacent the path aownstream o~ the electrode~ to measure the ef~ectiveness o~ the treatment o~ foil.
By way of e~ample an embodiment of the invention wiIl now be described with reference to the accompanying drawings ln which:
~igure 1 i~ a schematic side view of an apparatus ior implanting a charge in an electret foil;
Figureg 2A and 2B are graph# showing the variation o~ the electret charge implanted according to the voltage applied to the foil for the method embodying the invention and a previously proposed method; and Figures ~A and 3B are graphs showing the variation across a ~trip of foil of the electret charge implanted for the method embodying the invention and a previou~ly proposed method.
- The apparatus shown in Figure 1 includes an electret~oil ~upply spool 1, electrically conducting rollers 2, 3, 4, 5 and 6, an electr~cally conducting roller 7 electricall~
11508~6 connected to earth, an electrostatic measuring probe 8 a guide roller 9, and a take-up spool 10. The apparatu~
i8 housed in a chamber (not shown) having a filtered air unit to maintain the chamber full of clean air.
A strip of ~EP Teflon (Trade Mark) foil 11 is wound on the 8upply spool 1 and is prov~ded with an aluminised surface 12 on one face which is located on the inner sids of the foil when the foil i8 on the supply spool. The foil 11 passes from the supply spool 1 over the rollers 2, 3, 4, 5 and 6, around the sarthed roller 7 under the guide roller 9 and onto the take-up spool 10.
The rollers 2, 3, 4, 5 and 6 ~re each connected to a respective point of a potential divider netw~rk consisting - of resistors R1, R2, R3, R4 and R5 connected in series be-tween earth B and a voltage source V. The full voltage from the source V i9 applied to the roller 6 and proportions o~ the full voltage are applied to the rollers`2, 3, 4 and 5.
In the particular example of the invention being de~cribed the resistor R1 i8 40 Ml and the resistors R2, R3, R4 and R5 are each 10 M~so the voltages applied to the rcllers
for implanting an electret charge into a foil capable of retaining an effective electret charge.
It has been proposed to charge a strip of electret foil by passing one face of the ~trip over an electrode connected to a source of high voltage while making electrical contact with the other face of the strip so that an electric field is applied acros~ the foil.
Normally the electric field is applied while the electret foil i8 at an elevated temperature but in our copending British patent application No. 34018/78 published on 28th February 1979 under No. 2002961, there i~ de~cribed a proposal for charging a st~ip of electret foil at room temperature in which the electrode over which the strip is passed i~ a knife edge.
We have found that there are some disadvantage~
with the~e proposed charging methods. Fir~t we have found that the magnitude of the electret charge implan-ted into the material will vary from one batch of material to another, even though the charging conditions are apparently identical. Secondly, we have found that within a single strip of film there is a variation over the width and length of the strip of the magnitude of implanted electret charge. When the electret foil i8 employed, for example in the production of microphone transd~cers, the variation in electret charge of the foil resultQ in variation in the sen itivity of the tranQducers and either this variation has to be ' 1150~16 tolerated or the transducers have to be individually te~ted adding significantly to their manufacturing co~t.
It i~ an object of the invention to provide an improved method and apparatus for implanting an electret charge into a foil capable of retaining an effective electret charge.
According to the invention there is provided a method of implanting an electret charge into a foil capable of retaining an effective electret charge, - the method including applying a fir~t electric field and thereafter a second electric field acro~s the foil, the Qecond electric field being of greater magnitude than the first, whereby an effective electret charge is implanted into the foil.
We have found that the uneven electret charging mentioned above arises because during the manufacturing process the foil has an adventitiou~ electret charge implanted into it due to the high electrostatic voltage~
produced during mechanical handling and rolling of the foil. Any area of the foil that has this adventitious elect~et charge in it before charging will in the fir~t charging proces~ accept a different amount of charge from the knife edge than a non-charged area of foil, ~ince the effective electric field applied to the adventitiously charged area differs from that applied to the non-charged area. By charging the foil progres-sivel~f all of the foil is first charged to not less than ., , about the highest electret charge implanted during manufacture and i~ then further charged to the required final level. Since for the further charging, the foil starts with a relatively even electret charge the final charge implanted into the foil is very much more even than if the foil i8 subjected to only one electric fie~d.
Preferably at lea~t three electric fields are applied successively across the foil, the magnitude of the electric field~ increasing progre~ively, In one 10 embodiment of the invention five electric fields are applied ~uccessively across the foil. With five electric fields the implantation of charge is-Qubstantially even over the whole width and length of the electret foil.
In~tead of applying a succession of discrete and progressively greater electric fields to the electret foil, the magnitude of the electric field may be increased continuously from a fir~t value up to the maximum electric field to be applied.
The method may ~e carried out as a continuous 20 process. In this ca~e the charging of the foil in a succes~ion of discrete stage~ may be achieved by passing the electret foil over a series of electrodes maintained at progreQsively higher positive or negative potentialQ.
The charging of the foil by a continuously increasing electric field may ~e achieved ~y passing the electret foil over the surface of a resistive element having one end maintained at a higher positive or negative potential than the other end, there being a contin~ou~
11508~6 change in potential along the element from one end to the other.
As an alternative, the method may be carried out by pas~ing the foil over an electrode at a fir~t po-~itive or negative potential and then passing the foil over the same electrode at a second positive or negative potential higher than the first potential.
The greatest electric field applied acro~s the electret foil may lie in the range of from about 30 to 1o about 100 MV/m. In the case of a foil of 12.5 mm thick-ness this field is achieved by applying from about 375 to about 1250 volt~ across the foil.
The electrodes by which the electric fields are applied may be electrically conducting rollers.
The foil may be provided with a metallised surface on one face and this face may be pas3ed over an electri-- cally conducting roller by which the electric field is applied. The electrically conducting roller may be at earth potential.
The electret foil may be polytetrafluoroethylene, for example that sold under the trademark FEP Teflon.
Alternative materials which may for example be u~ed are polycarbonates or Mylar (RTM).
According to another aspect of the invention there is provided an electroacoustic transducer including an elec-tret foil as defined a~ove. The transducer may be incorporated in a telephone.
According to another aQpect of the invention there is provided an apparatu~ for implanting an effective electret charge into a foil capRble of retaining an effective electret charge, the apparatu~ including:
mean~ defining a path for a Qtrip of foil, a plurality of electrode-~ disposed along one ~ide of the path of the foil for making electrical contact with one face of the ~trip of foil, electrical contact mean~ on the-other side of the path for making electrical contact with the other face of the strip of foil, and means for applying a voltage between the elec-trodes and the electrical contact mean~, the arrange-; ment being such that the voltage applied to the electrode-~ is of greater magnitude towards the down-stream end of the path.
The plurality of electrode~ preferably comprises at lea~t three electrodes, the voltage applied to the electrode~ increaQing progre~ively towards the downQtream end of the path. The electrode~ may each be connected to a reQpective point in a potential divider network.
'`~' ~150816 A ~irQt spool ma~ be provided at the beginning oi the path for storing a strip of foil to be treated. A
second spool may be provided at the end of the path ~or recei~ing the ætrip of foil after treatment. The second spool may be connected to drive means to draw foil along the path. The first spool may be provided with a brake for ten~ioning foil along the path.
An electro~tatic measuring probe ma~ be located adjacent the path aownstream o~ the electrode~ to measure the ef~ectiveness o~ the treatment o~ foil.
By way of e~ample an embodiment of the invention wiIl now be described with reference to the accompanying drawings ln which:
~igure 1 i~ a schematic side view of an apparatus ior implanting a charge in an electret foil;
Figureg 2A and 2B are graph# showing the variation o~ the electret charge implanted according to the voltage applied to the foil for the method embodying the invention and a previously proposed method; and Figures ~A and 3B are graphs showing the variation across a ~trip of foil of the electret charge implanted for the method embodying the invention and a previou~ly proposed method.
- The apparatus shown in Figure 1 includes an electret~oil ~upply spool 1, electrically conducting rollers 2, 3, 4, 5 and 6, an electr~cally conducting roller 7 electricall~
11508~6 connected to earth, an electrostatic measuring probe 8 a guide roller 9, and a take-up spool 10. The apparatu~
i8 housed in a chamber (not shown) having a filtered air unit to maintain the chamber full of clean air.
A strip of ~EP Teflon (Trade Mark) foil 11 is wound on the 8upply spool 1 and is prov~ded with an aluminised surface 12 on one face which is located on the inner sids of the foil when the foil i8 on the supply spool. The foil 11 passes from the supply spool 1 over the rollers 2, 3, 4, 5 and 6, around the sarthed roller 7 under the guide roller 9 and onto the take-up spool 10.
The rollers 2, 3, 4, 5 and 6 ~re each connected to a respective point of a potential divider netw~rk consisting - of resistors R1, R2, R3, R4 and R5 connected in series be-tween earth B and a voltage source V. The full voltage from the source V i9 applied to the roller 6 and proportions o~ the full voltage are applied to the rollers`2, 3, 4 and 5.
In the particular example of the invention being de~cribed the resistor R1 i8 40 Ml and the resistors R2, R3, R4 and R5 are each 10 M~so the voltages applied to the rcllers
2, 3, 4 and 5 are ~ and ~ of the full voltage res-pectively.
The treatment of the foil is carried out at ambient temperature as a continuous process. The foil i9 drawn by the take-up s~ool 10 from the supply spool 1, under tension 11508~6 controlled by a brake (not shown), which may be an electro-motive brake, on the supply spool. The take-up spool 10 i~ driven by a motor (not shown), the speed of which may be adjusted by an operator. The foil passes around the roller~ 2, ~, 4, 5 and 6 which are arranged in an arc and then passe~ around the earthed roller 7 which makes electrical contact with the aluminised surface 12 i of the foil and thus en~ures that the ~luminised surface 12 i8 maintained at earth potential, not only in the ~lcin-ity of the roller 7 but along the entire length of the film.
After passing around the roller~7, the film passes under the guide roller 9 and i8 wound onto the take-up spool 16.
The charging of the foil 11 is monitored by the electrostatic measuring probe 8 which scans the surface potential of the complete width of the film. ~he degree of uniformit~ of potential is indicative of the evennesR
of charging. A~ the foil 11 is wound onto the take-up spool 10 the electro~tatic charge on the non-aluminised surface of the foil 10 leaks to earth by virtue of the con-tact of that surface with the aluminised surface of an adJacent layer of foil wound on the spool.
Te~t~ have been conducted on a film o~ 12.5 ym thickne~s 11508~
-- 10 _ using the apparatus shown in Figure 1 and var~ing the voltage of the voltage source V. Figure 2A æhows the results oi these tests,the vertical a~is of the graph being the electret voltage (measured in volts) implanted into the foil and the horizonta7 a~is being the voltage oi the voltage source V. Figure 2B shows the results o~
tests on the sPme materi~7 but using a ~ingle knife edge to charge the foil.
For both ~et~ of tests the electrst voltage and variation in the electret voltage impl~nted into the foil was measured. The vertical daæhed lines in Figures 2~
and 2~ show the total range of electret voltages implanted by a given treatment. It can easily be seen from comparison oi Figures 2A and 2B show that a more even distribution o~
charge i~ obtained b~ employing progressive charging than by employing a ~ingle kniie edge. Thi~ point iB further demonstrated b~ Figures 3~ and 3B in each of which the vertical axis is the electret voltage (measured $n volts) implanted into the ~oil and the horizontal a~is is the dis-tance acros~ the width of the electret film at which theelectret vo7tage is measured. ~he re~ults of Figure 3A were obtained uslng the apparatu~ of Fi~ure 1 and applying a voltage of - 800 volts ~rom the voltage source V acro~s 8 ~oil o~ 75 mm width and 12.5 pm thickness. The results o~
Figure 3B were obtained on the same ~oil but using a æingle knl~e edge as the charging electrodeJ the knife edge being maintained at a voltage of - 800 Volts. Again it will be seen that a more even distribution of charge iB
obtained by employing progressive charging than by employ-ing a single electrode.
The method and apparatus described above enable a more even ch~rge charge distribution to be obtained in the electret foil, and the electret voltage implanted i8 substantially independent o~ any adventitious electret i 10 charge implanted during manufacture of the foil and of varia-tions in the thickness o~ the ~oil.
The use o~ rollers as the electrodes enables good I electrical contact to be made with the foil and also minimises . .
the friction on the foil as it passes through the apparatus.
~he method and apparatus described above relato to an electret ~oil of 12.5 ~m thickness and 75 mm width.
~owever the method and apparatus are equally suitable for charging foils of other widths and thicknesse~ which may be chosen according to the p~rpo3e for which the ~oil i8 ; required. a The provision of/metallised ~urface on one ~ace of the electret foil ~aci~itates the making o~ a good electrical contact with thi~ ~ace of the f oil but it i8 not essential.
If the met~ ed surface is omitted contact can be made ¦ 25 b~ electrically conducting earthed roller~ po~itioned opposite each of the rollers connected to the voltage source.
.
~150816 In~tead o~ providing a ~eries o~ roller~ along the electret foil path maintained at progressivel~ higher potentials a continuous increase in potentlal-ma~ be provided along the path. This may be achieved by providing a belt o~ resistive material passing around two electricall~
conducting roller~ and runn ng along the path o~ the ioil between the rollers, a voltage ~ource being connected to the downstream roller and the upstream roller being connected through a re~i~tor to earth.
It is possible to carry out the method oi the inven-tion u~ing a single electrode. In this case the electret foil may be pa~6ed over the electrode wh~le it is maintained at a first potential and the~pa~sed one or more iurther times over the electrode with the electrode maintained at a higher potential than on the previous pass.
The charging o~ the ~oil described with re~erence to the drawings is carried out at room temperature, but it will be under~tood that the treatment could also be carried out at a higher temperature.
. ' .
,, , ll i
The treatment of the foil is carried out at ambient temperature as a continuous process. The foil i9 drawn by the take-up s~ool 10 from the supply spool 1, under tension 11508~6 controlled by a brake (not shown), which may be an electro-motive brake, on the supply spool. The take-up spool 10 i~ driven by a motor (not shown), the speed of which may be adjusted by an operator. The foil passes around the roller~ 2, ~, 4, 5 and 6 which are arranged in an arc and then passe~ around the earthed roller 7 which makes electrical contact with the aluminised surface 12 i of the foil and thus en~ures that the ~luminised surface 12 i8 maintained at earth potential, not only in the ~lcin-ity of the roller 7 but along the entire length of the film.
After passing around the roller~7, the film passes under the guide roller 9 and i8 wound onto the take-up spool 16.
The charging of the foil 11 is monitored by the electrostatic measuring probe 8 which scans the surface potential of the complete width of the film. ~he degree of uniformit~ of potential is indicative of the evennesR
of charging. A~ the foil 11 is wound onto the take-up spool 10 the electro~tatic charge on the non-aluminised surface of the foil 10 leaks to earth by virtue of the con-tact of that surface with the aluminised surface of an adJacent layer of foil wound on the spool.
Te~t~ have been conducted on a film o~ 12.5 ym thickne~s 11508~
-- 10 _ using the apparatus shown in Figure 1 and var~ing the voltage of the voltage source V. Figure 2A æhows the results oi these tests,the vertical a~is of the graph being the electret voltage (measured in volts) implanted into the foil and the horizonta7 a~is being the voltage oi the voltage source V. Figure 2B shows the results o~
tests on the sPme materi~7 but using a ~ingle knife edge to charge the foil.
For both ~et~ of tests the electrst voltage and variation in the electret voltage impl~nted into the foil was measured. The vertical daæhed lines in Figures 2~
and 2~ show the total range of electret voltages implanted by a given treatment. It can easily be seen from comparison oi Figures 2A and 2B show that a more even distribution o~
charge i~ obtained b~ employing progressive charging than by employing a ~ingle kniie edge. Thi~ point iB further demonstrated b~ Figures 3~ and 3B in each of which the vertical axis is the electret voltage (measured $n volts) implanted into the ~oil and the horizontal a~is is the dis-tance acros~ the width of the electret film at which theelectret vo7tage is measured. ~he re~ults of Figure 3A were obtained uslng the apparatu~ of Fi~ure 1 and applying a voltage of - 800 volts ~rom the voltage source V acro~s 8 ~oil o~ 75 mm width and 12.5 pm thickness. The results o~
Figure 3B were obtained on the same ~oil but using a æingle knl~e edge as the charging electrodeJ the knife edge being maintained at a voltage of - 800 Volts. Again it will be seen that a more even distribution of charge iB
obtained by employing progressive charging than by employ-ing a single electrode.
The method and apparatus described above enable a more even ch~rge charge distribution to be obtained in the electret foil, and the electret voltage implanted i8 substantially independent o~ any adventitious electret i 10 charge implanted during manufacture of the foil and of varia-tions in the thickness o~ the ~oil.
The use o~ rollers as the electrodes enables good I electrical contact to be made with the foil and also minimises . .
the friction on the foil as it passes through the apparatus.
~he method and apparatus described above relato to an electret ~oil of 12.5 ~m thickness and 75 mm width.
~owever the method and apparatus are equally suitable for charging foils of other widths and thicknesse~ which may be chosen according to the p~rpo3e for which the ~oil i8 ; required. a The provision of/metallised ~urface on one ~ace of the electret foil ~aci~itates the making o~ a good electrical contact with thi~ ~ace of the f oil but it i8 not essential.
If the met~ ed surface is omitted contact can be made ¦ 25 b~ electrically conducting earthed roller~ po~itioned opposite each of the rollers connected to the voltage source.
.
~150816 In~tead o~ providing a ~eries o~ roller~ along the electret foil path maintained at progressivel~ higher potentials a continuous increase in potentlal-ma~ be provided along the path. This may be achieved by providing a belt o~ resistive material passing around two electricall~
conducting roller~ and runn ng along the path o~ the ioil between the rollers, a voltage ~ource being connected to the downstream roller and the upstream roller being connected through a re~i~tor to earth.
It is possible to carry out the method oi the inven-tion u~ing a single electrode. In this case the electret foil may be pa~6ed over the electrode wh~le it is maintained at a first potential and the~pa~sed one or more iurther times over the electrode with the electrode maintained at a higher potential than on the previous pass.
The charging o~ the ~oil described with re~erence to the drawings is carried out at room temperature, but it will be under~tood that the treatment could also be carried out at a higher temperature.
. ' .
,, , ll i
Claims (17)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of implanting an electret charge into a foil capable of retaining an effective electret charge, the method including applying a first electric field and thereafter a second electric field across the foil, the second electric field being of greater magnitude than the first, whereby an effective electret charge is implanted into the foil.
2. A method as claimed in claim 1 in which at least three electric fields are applied successively across the foil, the magnitude of the electric fields increas-ing progressively.
3. A method as claimed in claim 2 in which five electric fields are applied successively across the foil.
4. A method as claimed in claim 1 in which the magni-tude of the electric field applied across the foil is increased continuously from a first value up to the maximum electric field to be applied.
5. . A method as claimed in claim 1 wherein the method is carried out as a continuous process.
6. A method as claimed in claim 5 in which the electret foil is passed over a series of electrodes maintained at progressively higher positive or negative potentials.
7. A method as claimed in claim 5 in which the electret foil is passed over the surface of a resistive element having one end maintained at a higher positive or negative potential than the other end, there being a continuous change in potential along the element from one end to the other.
8. A method as claimed in claim 1 in which the foil is passed over an electrode at a first positive or negative potential and then passed over the same electrode at a second positive or negative potential higher than the first potential.
9. A method as claimed in claim 1 in which the greatest electric field applied across the electret foil lies in the range of from about 30 to about 100 MV/m.
10. A method as claimed in claim 6 in which the electrodes by which the electric fields are applied are electrically conducting rollers.
11. A method as claimed in claim 1 in which the foil is provided with a metallised surface on one face and this face is passed over an electrically conducting roller by which the electric field is applied.
12. A method as claimed in claim 11 in which the electrically conducting roller is at earth potential.
13. A method as claimed in claim 1 in which the electret foil is polytetrafluoroethylene.
14. An apparatus for implanting an effective electret charge into a foil capable of retaining an effective electret charge, the apparatus including:
means defining a path for a strip of foil, a plurality of electrodes disposed along one side of the path of the foil for making electrical contact with one face of the strip of foil, electrical contact means on the other side of the path for making electrical contact with the other face of the strip of foil, and means for applying a voltage between the electrodes and the electrical contact means, the arrangement being such that the voltage applied to the electrodes is of greater magnitude towards the downstream end of the path.
means defining a path for a strip of foil, a plurality of electrodes disposed along one side of the path of the foil for making electrical contact with one face of the strip of foil, electrical contact means on the other side of the path for making electrical contact with the other face of the strip of foil, and means for applying a voltage between the electrodes and the electrical contact means, the arrangement being such that the voltage applied to the electrodes is of greater magnitude towards the downstream end of the path.
15. An apparatus as claimed in claLm 14 in which the plurality of electrodes comprises at least three electrodes, the voltage applied to the electrodes increasing progressively towards the downstream end of the path.
16. An apparatus as claimed in claim 15 in which the electrodes are each connected to a respective point in a potential divider network.
17. An apparatus as claimed in claim 16 in which a first spool is provided at the beginning of the path for storing a strip of foil to be treated and has a brake for tensioning foil along the path.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7923737 | 1979-07-06 | ||
| GB7923737 | 1979-07-06 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1150816A true CA1150816A (en) | 1983-07-26 |
Family
ID=10506367
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000354480A Expired CA1150816A (en) | 1979-07-06 | 1980-06-20 | Method and apparatus for implanting a charge in an electret foil |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4348711A (en) |
| EP (1) | EP0022630B1 (en) |
| JP (1) | JPS5635405A (en) |
| AT (1) | ATE3344T1 (en) |
| CA (1) | CA1150816A (en) |
| DE (1) | DE3063102D1 (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4512940A (en) * | 1982-12-16 | 1985-04-23 | Ncr Corporation | Method and apparatus for the production of electret material |
| US5401446A (en) * | 1992-10-09 | 1995-03-28 | The University Of Tennessee Research Corporation | Method and apparatus for the electrostatic charging of a web or film |
| JP2007210398A (en) * | 2006-02-08 | 2007-08-23 | Nissan Motor Co Ltd | Spring seat of suspension |
| AU2008232361B2 (en) | 2007-03-23 | 2013-05-16 | Allegiance Corporation | Fluid collection and disposal system and related methods |
| US9889239B2 (en) | 2007-03-23 | 2018-02-13 | Allegiance Corporation | Fluid collection and disposal system and related methods |
| CN114953422A (en) * | 2022-05-24 | 2022-08-30 | 潍坊新声悦尔电子科技有限公司 | High-temperature-resistant back plate continuous processing device and processing technology thereof |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2757165A (en) * | 1954-09-02 | 1956-07-31 | Monsanto Chemicals | Vinyl acetate/acrylonitrile/styrene terpolymers |
| GB1267535A (en) * | 1968-03-19 | 1972-03-22 | Iwatsu Electric Co Ltd | Electrophotographic process and apparatus |
| NL143362B (en) * | 1968-07-10 | 1974-09-16 | Tno | METHOD OF FORMING A ONE-SIDED METALLIZED ELECTRICAL PHOELY, AND SUCH AN ELECTRICAL FOELY FORMED ACCORDING TO THIS METHOD. |
| US3678350A (en) * | 1971-04-19 | 1972-07-18 | Xerox Corp | Electric charging method |
| US3684364A (en) * | 1971-06-24 | 1972-08-15 | Xerox Corp | Lift off electrode |
| NL7210088A (en) * | 1972-07-21 | 1974-01-23 | ||
| JPS523632B2 (en) * | 1972-08-26 | 1977-01-28 | ||
| US3873895A (en) * | 1973-12-05 | 1975-03-25 | Xerox Corp | Technique for charging dielectric surfaces to high voltage |
| NL160303C (en) * | 1974-03-25 | 1979-10-15 | Verto Nv | METHOD FOR MANUFACTURING A FIBER FILTER |
| US4089034A (en) * | 1976-04-30 | 1978-05-09 | Minnesota Mining And Manufacturing Company | Machine and method for poling films of pyroelectric and piezoelectric material |
| GB2002961A (en) * | 1977-08-22 | 1979-02-28 | Post Office | Implanting an electret charge in a foil material |
-
1980
- 1980-06-20 CA CA000354480A patent/CA1150816A/en not_active Expired
- 1980-06-25 EP EP80302129A patent/EP0022630B1/en not_active Expired
- 1980-06-25 DE DE8080302129T patent/DE3063102D1/en not_active Expired
- 1980-06-25 US US06/162,904 patent/US4348711A/en not_active Expired - Lifetime
- 1980-06-25 AT AT80302129T patent/ATE3344T1/en not_active IP Right Cessation
- 1980-07-02 JP JP9049780A patent/JPS5635405A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| DE3063102D1 (en) | 1983-06-16 |
| JPS6229887B2 (en) | 1987-06-29 |
| JPS5635405A (en) | 1981-04-08 |
| EP0022630A1 (en) | 1981-01-21 |
| ATE3344T1 (en) | 1983-05-15 |
| EP0022630B1 (en) | 1983-05-11 |
| US4348711A (en) | 1982-09-07 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |